I am quite familiar with this problem. What everyone should be aware of is that all and I repeat ALL 2004 and 2005 RX 330's are affected by this problem because it is an inherent problem with the design of the vehicle. If you say your's doesn't do it, its just because either you haven't noticed it or you haven't experienced the conditions that cause it to happen.
Specifically this is a thumping from the rear hatch when going up a banked curb such as on a drive way. I have only ever heard it when making a right hand turn. If you make a left hand turn to get up your driveway, chances are you won't hear it. It is not from the suspension, trust me, I had mine replaced when I first noticed this and it had no effect. After this, I had a very sharp technician road test with me and we noticed that the noise fails to occur when the hatch is left open (try this at home). We looked even closer and noticed that at the very instant that the noise occurs, the hatch gets dislocated out of alignment for a brief period and then goes back into place....hence the thump.
The problem is that when the vehicle undergoes torsion (twisting) force, there is only one anchor point at the base of the hatch, and hence it pops out of place for a brief moment and makes a thump. Once the vehicle levels out again, it goes back into place quickly.
We all have this problem and should all be complaining to our dealerships about it otherwise they won't have an incentive to fix it. I am curious as to how much money Lexus has lost replacing suspensions that were not faulty.
